Gas supply system, plasma processing apparatus, and control method for gas supply system

ABSTRACT

When a gas supplied to a gas injection unit is switched from a first processing gas to a second processing gas, a controller of a gas supply system performs control to open a first supply on/off valve connected to the gas injection unit and provided in a first gas supply line for supplying the first processing gas and a second exhaust on/off valve provided in a first gas exhaust line branched from the first gas supply line, close a second supply on/off valve connected to the gas injection unit and provided in a second gas supply line for supplying the second processing gas and a first exhaust on/off valve provided in a second gas exhaust line branched from the second gas supply line; and then open the second supply on/off valve and the first exhaust on/off valve and close the first supply on/off valve and the second exhaust on/off valve.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation application of U.S. application Ser.No. 16/979,793 filed on Sep. 10, 2020, which is a continuation of 35 USC§ 371 National Phase Application No. PCT/JP2019/023994 filed Jun. 18,2019, which claims priority from Japanese Patent Application No.2018-126127 filed on Jul. 2, 2018, all of which are incorporated hereinin their entirety by reference is claimed to each.

TECHNICAL FIELD

The present disclosure relates to a gas supply system, a plasmaprocessing apparatus, and a control method for the gas supply system.

BACKGROUND

For example, in Patent Document 1, a gas diffusion chamber in a showerhead is divided into a plurality of spaces by partition walls. Further,gas distribution pipes communicating with the respective spaces andvalves that are open and closed to allow adjacent gas distribution pipesto communicate with each other are provided. Patent Document 1 disclosesa technique that a processing gas supplied to each of the spaces isswitched by opening and closing the valves.

PRIOR ART

Patent Document 1: Japanese Patent Application Publication No.2012-114275

The present disclosure provides a technique capable of stably andrapidly switching a processing gas.

SUMMARY

In accordance with an aspect of the present disclosure, there isprovided a gas supply system including: a gas injection unit that isdisposed to face a substrate support on which a target object is to beplaced and configured to inject a gas from a plurality of gas injectionholes formed on a facing surface of the gas injection unit that facesthe substrate support; a first gas supply line that is connected to thegas injection unit and configured to supply a first processing gas; asecond gas supply line that is connected to the gas injection unit andconfigured to supply a second processing gas; a first gas exhaust linethat is branched from the first gas supply line and configured toexhaust the first processing gas flowing through the first gas supplyline to a gas exhaust mechanism; a second gas exhaust line that isbranched from the second gas supply line and configured to exhaust thesecond processing gas flowing through the second gas supply line to thegas exhaust mechanism; a first supply on/off valve that is disposed at adownstream side of a branch point of the first gas supply line where thefirst gas exhaust line is branched and configured to switch an ON/OFFstate of the first gas supply line; a second supply on/off valve that isdisposed at a downstream side of a branch point of the second gas supplyline where the second gas exhaust line is branched and configured toswitch an ON/OFF state of the second gas supply line; a first exhauston/off valve configured to switch an ON/OFF state of the first gasexhaust line; a second exhaust on/off valve configured to switch anON/OFF state of the second gas exhaust line; and a controller configuredto control the first supply on/off valve and the second exhaust on/offvalve to be in an open state and the second supply on/off valve and thefirst exhaust on/off valve to be in a closed state, and then control thesecond supply on/off valve and the first exhaust on/off valve to be inan open state and the first supply on/off valve and the second exhauston/off valve to be in a closed state when the gas supplied to the gasinjection unit is switched from the first processing gas to the secondprocessing gas, and control the second supply on/off valve and the firstexhaust on/off valve to be in the open state and the first supply on/offvalve and the second exhaust on/off valve to be in the closed state, andthen control the first supply on/off valve and the second exhaust on/offvalve to be in the open state and the second supply on/off valve and thefirst exhaust on/off valve to be in the closed state when the gassupplied to the gas injection unit is switched from the secondprocessing gas to the first processing gas.

In accordance with the aspect of the present disclosure, it is possibleto switch the processing gas stably and rapidly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view showing an example of a schematicconfiguration of a plasma processing apparatus according to anembodiment.

FIG. 2 shows an example of a schematic configuration of a gas supplysystem according to an embodiment.

FIG. 3 shows an example of a schematic process of atomic layer etchingaccording to the embodiment.

FIG. 4 shows an example of a schematic configuration of supply paths fora processing gas in the gas supply system according to the embodiment.

FIG. 5 shows an example of a processing gas ratio according to theembodiment.

FIG. 6 shows an example of a flow split control of the processing gasaccording to the embodiment.

FIG. 7 shows an example of a relationship between a gas pressure and aflow rate according to the embodiment.

FIG. 8A shows a switching operation in the gas supply system accordingto the embodiment.

FIG. 8B shows the switching operation in the gas supply system accordingto the embodiment.

FIG. 9A shows a backflow of a processing gas.

FIG. 9B shows the backflow of a processing gas.

FIG. 9C shows the backflow of a processing gas.

FIG. 10A shows an example of pressure control for the switchingoperation in the gas supply system according to the embodiment.

FIG. 10B shows an example of pressure control for the switchingoperation in the gas supply system according to the embodiment.

FIG. 11 shows an example of pressure control for the switching operationin the gas supply system according to the embodiment.

FIG. 12A shows an example of control flow of a control method for thegas supply system according to the embodiment.

FIG. 12B shows an example of the control flow of the control method forthe gas supply system according to the embodiment.

FIG. 12C shows an example of the control flow of the control method forthe gas supply system according to the embodiment.

FIG. 12D shows an example of the control flow of the control method forthe gas supply system according to the embodiment.

FIG. 12E shows an example of the control flow of the control method forthe gas supply system according to the embodiment.

FIG. 12F shows an example of the control flow of the control method forthe gas supply system according to the embodiment.

FIG. 12G shows an example of the control flow of the control method forthe gas supply system according to the embodiment.

DETAILED DESCRIPTION

Hereinafter, a gas supply system, a plasma processing apparatus, and acontrol method for the gas supply system according to embodiments of thepresent disclosure will be described in detail with reference to theaccompanying drawings. However, the following embodiments are notintended to limit the gas supply system, the plasma processingapparatus, and the control method for the gas supply system of thepresent disclosure.

In a plasma processing apparatus for performing a plasma treatment, aplurality of processing gases may be used and switched to perform theplasma treatment. For example, an atomic layer etching (ALE) that etchesan etching target film layer by layer has been suggested as a type ofetching method. In the atomic layer etching, the etching target film isetched using plasma by repeating a step of adsorbing an adsorbategenerated based on a first processing gas on the etching target film anda step of activating the adsorbate using a second processing gas.

In such a plasma processing apparatus that performs the plasma treatmentby switching the plurality of processing gases, it is desired that theprocessing gases are stably and rapidly switched.

<Configuration of the Plasma Processing Apparatus>

A plasma processing apparatus 10 according to an embodiment will bedescribed. FIG. 1 is a cross sectional view showing a schematicconfiguration of a plasma processing apparatus according to anembodiment. The plasma processing apparatus 10 shown in FIG. 1 is acapacitively-coupled parallel-plate plasma etching apparatus. The plasmaprocessing apparatus 10 includes a substantially cylindrical processingchamber 12.

A substrate support 16 is disposed in the processing chamber 12. Thesubstrate support 16 includes a support member 18 and a base 20. A topsurface of the support member 18 is a substrate supporting surface onwhich a target object to be subjected to a plasma treatment is placed.In the present embodiment, a wafer W that is the target object for theplasma etching is placed on the top surface of the support member 18.The base 20 has a substantially disc shape and a main part thereof ismade of a conductive metal such as aluminum. The base 20 serves as alower electrode. The base is supported by a support portion 14. Thesupport portion 14 is a cylindrical member vertically extending upwardfrom the bottom of the processing chamber 12.

A first radio frequency power supply HFS is electrically connected tothe base 20 through a matching unit MU1. The first radio frequency powersupply HFS is a power supply configured to generate a radio frequencypower for plasma generation having a frequency in a range from 27 to 100MHz, e.g., 40 MHz. The matching unit MU1 includes a circuit for matchingan output impedance of the first radio frequency power supply HFS withan input impedance of a load side (base 20 side).

A second radio frequency power supply LFS is electrically connected tothe base 20 through a matching unit MU2. The second radio frequencypower supply LFS is configured to generate a radio frequency power(radio frequency bias power) for attracting ions into the wafer W andapply the radio frequency bias power to the base 20. A frequency of theradio frequency bias power is within a range from 400 kHz to 13.56 MHz,e.g., 3 MHz. The matching unit MU2 includes a circuit for matching anoutput impedance of the second radio frequency power supply LFS with aninput impedance of the load side (base 20 side).

The support member 18 is disposed on the base 20. The support member 18is, for example, an electrostatic chuck. The wafer W is attracted to andheld on the support member 18 by an electrostatic force such as aCoulomb force. The support member 18 includes an electrode E1 forelectrostatic adsorption in a main body portion formed of ceramic. A DCpower supply 22 is electrically connected to the electrode E1 through aswitch SW1. The support member 18 may further include a heater fortemperature control of the wafer W.

A focus ring FR is disposed on a top surface of the base 20 to surroundthe support member 18. The focus ring FR is provided to improveuniformity of a plasma treatment. The focus ring FR is formed of amaterial appropriately selected depending on the plasma treatment to beperformed. For example, the focus ring FR may be formed of silicon orquartz.

A coolant channel 24 is formed in the base 20. The coolant is suppliedto the coolant channel 24 from a chiller unit provided outside of theprocessing chamber 12 through a line 26 a. The coolant supplied to thecoolant channel 24 returns to the chiller unit through a line 26 b.

An upper electrode 30 serving as a shower head for supplying a gastoward the wafer W is disposed in the processing chamber 12. In theplasma processing apparatus 10 according to the embodiment, the upperelectrode 30 corresponds to the gas injection unit. The upper electrodeis disposed above the substrate support 16 to be opposite to the base20. The base 20 and the upper electrode 30 are arranged to besubstantially parallel to each other. A processing space S where plasmafor performing a plasma treatment on the wafer W is formed between theupper electrode and the lower electrode 20.

The upper electrode 30 is supported at an upper portion of theprocessing chamber 12 via an insulating shield member 32. The upperelectrode 30 may include an electrode plate 34 and an electrode holder36. The electrode plate 34 faces the processing space S, and a pluralityof gas injection holes 34 a are formed in the electrode plate 34.

The electrode holder 36 is made of a conductive material such asaluminum and is configured to detachably hold the electrode plate 34.The electrode holder 36 may have a water-cooling structure. A gasdiffusion chamber 37 having a disc-shaped space is formed in theelectrode holder 36. The gas diffusion chamber 37 is divided into aplurality of spaces. For example, the gas diffusion chamber 37 isprovided with annular partition wall members 38. In the plasmaprocessing apparatus 10 according to the present embodiment, the gasdiffusion chamber 37 is divided into a plurality of spaces in the radialdirection by the partition wall members 38. For example, the gasdiffusion chamber 37 is divided into three zones of a gas diffusion zone37 c, a gas diffusion zone 37 e, and a gas diffusion zone 37 v torespectively correspond to a center portion that is a central portion ofthe wafer W, an edge portion that is a peripheral portion of the waferW, and a very edge portion that is an outermost edge portion of thewafer W. However, the number of zones defining the gas diffusion chamber37 is not limited to three and may be two or four or more. The gasdiffusion zone 37 c is a disc-shaped space. The gas diffusion zone 37 eis a ring-shaped space surrounding the gas diffusion zone 37 c. The gasdiffusion zone 37 v is a ring-shaped space surrounding the gas diffusionspace 37 e. A plurality of gas holes 36 b respectively communicatingwith the gas injection holes 34 a extend downward from each of the gasdiffusion zone 37 c, the gas diffusion zone 37 e, and the gas diffusionzone 37 v.

The plasma processing apparatus 10 is provided with a gas box 40 forsupplying various gases used for a plasma treatment. Further, a gassupply system 110 for supplying the gas supplied from the gas box 40 toeach of the gas diffusion zones 37 c, 37 e, and 37 v is connected to theelectrode holder 36. The details of the gas supply system 110 will bedescribed later.

The gas supplied to each of the gas diffusion zones 37 c, 37 e, and 37 vis injected into the processing space S through the gas holes 36 b andthe gas injection holes 34 a. By controlling the gas box 40 and the gassupply system 110, the plasma processing apparatus 10 can control theflow rate of the processing gas injected into the processing space Sfrom the gas injection holes 34 a of each of the gas diffusion zones 37c, 37 e, and 37 v.

At a lower portion in the processing chamber 12, a gas exhaust plate 48is provided between the support portion 14 and an inner wall of theprocessing chamber 12. The gas exhaust plate 48 may be formed by, forexample, coating an aluminum base with ceramic such as Y₂O₃. A gasexhaust port 12 e is provided below the gas exhaust plate 48 in theprocessing chamber 12. A gas exhaust device 50 is connected to the gasexhaust port 12 e through a gas exhaust line 52. The gas exhaust device50 includes a vacuum pump such as a turbo molecular pump so thatpressure in the processing chamber 12 can be reduced to a desired vacuumlevel. Further, a loading/unloading port 12 g for the wafer W isprovided at the sidewall of the processing chamber 12. Theloading/unloading port 12 g can be opened and closed by a gate valve 54.

The operation of the plasma processing apparatus 10 configured asdescribed above is integrally controlled by a controller 100. Thecontroller 100 is, for example, a computer and controls the individualcomponents of the plasma processing apparatus 10. The operation of theplasma processing apparatus 10 is integrally controlled by thecontroller 100.

The controller 100 includes a CPU, a process controller 101 thatcontrols the individual components of the plasma processing apparatus10, a user interface 102, and a storage unit 103.

The user interface 102 includes a keyboard through which a processmanager inputs commands to manage the plasma processing apparatus 10, adisplay for visualizing and displaying an operation status of the plasmaprocessing apparatus 10, and the like.

The storage unit 103 stores therein control programs (software) forimplementing various processes in the plasma processing apparatus 10under the control of the process controller 101 and/or recipes includingprocessing condition data and the like. Then, the process controller 101calls and executes a certain recipe from the storage unit 103 accordingto an instruction inputted through the user interface 102, so that adesired process is performed in the plasma processing apparatus 10 underthe control of the process controller 101. For example, the processcontroller 101 controls the individual components of the plasmaprocessing apparatus 10 to execute a control method of the gas supplysystem 110 to be described later. Further, the control programs and therecipes having the processing condition data may be stored in acomputer-readable storage medium (e.g., a hard disk, a CD, a flexibledisk, a semiconductor memory, or the like). Alternatively, the controlprograms and the recipes having the processing condition data may beused online by frequently transmitting from other devices through e.g.,a dedicated line.

Next, a configuration of the gas supply system according to theembodiment will be described. FIG. 2 shows an example of a schematicconfiguration of the gas supply system according to the embodiment. Inthe example of FIG. 2 , the gas diffusion zones 37 c, 37 e, and 37 vprovided in the upper electrode 30 are illustrated in a simplifiedmanner.

The gas box 40 has a gas source group 41 including various gas sourcesused for a plasma treatment such as plasma etching. The gas box 40includes, for example, a valve and a flow rate controller (not shown)for each of the gas sources of the gas source group 41. Further, the gasbox 40 is configured to supply one gas or a gas mixture of various gasesas a processing gas depending on the plasma treatment.

The gas supply system 110 is configured to distribute the processing gassupplied from the gas box 40 to be supplied to the gas diffusion zones37 c, 37 e, and 37 v.

In the plasma processing apparatus 10, a plurality of processing gasesmay be switched to perform a plasma treatment. For example, in atomiclayer etching, a step of adsorbing an adsorbate generated based on afirst processing gas on an etching target film with plasma and a step ofactivating the adsorbate with a second processing gas are repeated toetch the wafer W.

FIG. 3 shows an example of a schematic process of the atomic layeretching according to the embodiment. For example, in an A-process, theadsorbate generated based on the first processing gas is adsorbed on thewafer W. In a B-process, the adsorbate is activated by the secondprocessing gas to etch the wafer W. In the atomic layer etching, theA-process and the B-process are repeated until the desired etchingamount is obtained.

The gas supply system 110 according to the embodiment includes aplurality of supply paths for supplying the processing gas to the gasdiffusion zones 37 c, 37 e, and 37 v such that the processing gas can bestably and rapidly switched.

FIG. 4 shows an example of a schematic configuration of the supply pathsfor a processing gas in the gas supply system according to theembodiment. FIG. 4 shows the configuration of the supply paths forsupplying the first processing gas and the second processing gas usedfor the atomic layer etching. In FIG. 4 , for the sake of simplicity ofdescription, only the supply paths for supplying the processing gas tothe gas diffusion zones 37 c and 37 e are illustrated, and a supply pathfor supplying the processing gas to the gas diffusion zone 37 v isomitted. The configuration of the supply path for supplying theprocessing gas to the gas diffusion zone 37 v is similar to the supplypath for supplying the processing gas to each of the gas diffusion zones37 c and 37 e.

A gas supply line 111 and a gas supply line 112 are connected to the gasbox 40. The gas box 40 supplies the first processing gas, which is onegas or a gas mixture of various gases, to the gas supply line 111.Further, the gas box 40 supplies the second processing gas, which is onegas or a gas mixture of various gases, to the gas supply line 112. Forexample, the first processing gas is a CF-based gas, and the secondprocessing gas is a gas mixture in which a CF-based gas and a noble gasare mixed.

Each of the gas supply line 111 and the gas supply line 112 branchesinto the supply paths to the gas diffusion zones 37 c, 37 e, and 37 v.In the example of FIG. 4 , the gas supply line 111 branches into a gassupply line 113 c and a gas supply line 113 e. The gas supply line 112branches into a gas supply line 114 c and a gas supply line 114 e.

The gas supply line 113 c and the gas supply line 114 c are connected toa common line 115 c. The common line 115 c is connected to the gasdiffusion zone 37 c. The gas supply line 113 e and the gas supply line114 e are connected to a common line 115 e. The common line 115 e isconnected to the gas diffusion zone 37 e.

Further, a gas exhaust line 116 c is branched from the gas supply line113 c on the way to the common line 115 c. A gas exhaust line 116 e isbranched from the gas supply line 113 e on the way to the common line115 e. A gas exhaust line 117 c is branched from the gas supply line 114c on the way to the common line 115 c. A gas exhaust line 117 e isbranched from the gas supply line 114 e on the way to the common line115 e.

The gas exhaust line 116 c and the gas exhaust line 117 c are connectedto a common line 118 c. The gas exhaust line 116 e and the gas exhaustline 117 e are connected to a common line 118 e. The common line 118 cand the common line 118 e are connected to a gas exhaust mechanism. Thegas exhaust mechanism may be the gas exhaust device 50 or another gasexhaust device different from the gas exhaust device 50.

The first processing gas supplied to the gas supply line 111 is suppliedto the gas supply line 113 c and the gas supply line 113 e. The firstprocessing gas supplied to the gas supply line 113 c flows through thecommon line 115 c and reaches the gas diffusion zone 37 c. Further, thefirst processing gas supplied to the gas supply line 113 c reaches thegas exhaust mechanism through the gas exhaust line 116 c and the commonline 118 c. The first processing gas supplied to the gas supply line 113e flows through the common line 115 e and reaches the gas diffusion zone37 e. Further, the first processing gas supplied to the gas supply line113 e reaches the gas exhaust mechanism through the gas exhaust line 116e and the common line 118 e.

The second processing gas supplied to the gas supply line 112 issupplied to the gas supply line 114 c and the gas supply line 114 e. Thesecond processing gas supplied to the gas supply line 114 c flowsthrough the common line 115 c and reaches the gas diffusion zone 37 c.Further, the second processing gas supplied to the gas supply line 114 creaches the gas exhaust mechanism through the gas exhaust line 117 c andthe common line 118 c. The second processing gas supplied to the gassupply line 114 e flows through the common line 115 e and reaches thegas diffusion zone 37 e. Further, the second processing gas supplied tothe gas supply line 114 e reaches the gas exhaust mechanism through thegas exhaust line 117 e and the common line 118 e.

The gas supply line 113 c is provided with a flow rate control valve 131c capable of adjusting an opening degree thereof at an upstream side ofa branch point 119 c where the gas exhaust line 116 c is branched.Further, the gas supply line 113 c is provided with a supply on/offvalve 132 c for switching an ON/OFF state of the gas supply line 113 cat a downstream side of the branch point 119 c. The supply on/off valve132 c is provided with an orifice 138 having a predetermined diameter.

The gas supply line 113 e is provided with a flow rate control valve 131e capable of adjusting an opening degree thereof at an upstream side ofa branch point 119 e where the gas exhaust line 116 e is branched.Further, the gas supply line 113 e is provided with a supply on/offvalve 132 e for switching an ON/OFF state of the gas supply line 113 eat a downstream side of the branch point 119 e. The supply on/off valve132 e is provided with an orifice 138 having a predetermined diameter.

The common line 115 c is provided with a pressure gauge 141 c formeasuring a pressure of the gas supplied to the gas diffusion zone 37 c.The common line 115 e is provided with a pressure gauge 141 e formeasuring a pressure of the gas supplied to the gas diffusion zone 37 e.

The gas exhaust line 116 c is provided with an exhaust on/off valve 135c for switching an ON/OFF state of the gas exhaust line 116 c. The gasexhaust line 116 e is provided with an exhaust on/off valve 135 e forswitching an ON/OFF state of the gas exhaust line 116 e. Each of theexhaust on/off valve 135 c and the exhaust on/off valve 135 e isprovided with an orifice 138 having a predetermined diameter.

The gas supply line 114 c is provided with a flow rate control valve 133c capable of adjusting an opening degree thereof at an upstream of abranch point 120 c where the gas exhaust line 117 c is branched.Further, the gas supply line 114 c is provided with a supply on/offvalve 134 c for switching an ON/OFF state of the gas supply line 114 cat a downstream side of the branch point 120 c. The supply on/off valve134 c is provided with an orifice 138 having a predetermined diameter.

The gas supply line 114 e is provided with a flow rate control valve 133e capable of adjusting an opening degree thereof at an upstream side ofa branch point 120 e where the gas exhaust line 117 e is branched.Further, the gas supply line 114 e is provided with a supply on/offvalve 134 e for switching an ON/OFF state of the gas supply line 114 eat a downstream side of the branch point 120 e. The supply on/off valve134 e is provided with an orifice 138 having a predetermined diameter.

The gas exhaust line 117 c is provided with an exhaust on/off valve 136c for switching an ON/OFF state of the gas exhaust line 117 c. The gasexhaust line 117 e is provided with an exhaust on/off valve 136 e forswitching an ON/OFF state of the gas exhaust line 117 e. Each of theexhaust on/off valve 136 c and the exhaust on/off valve 136 e isprovided with an orifice 138 having a predetermined diameter.

The common line 118 c is provided with a pressure gauge 142 c formeasuring a pressure of the gas flowing to the gas exhaust mechanism.Further, the common line 118 c is provided with an exhaust flow ratecontrol valve 137 c capable of adjusting an opening degree thereof at adownstream side of the pressure gauge 142 c.

The common line 118 e is provided with a pressure gauge 142 e formeasuring a pressure of the gas flowing to the gas exhaust mechanism.Further, the common line 118 e is provided with an exhaust flow ratecontrol valve 137 e capable of adjusting an opening degree thereof at adownstream side of the pressure gauge 142 e.

In order to suppress the non-uniformity of the plasma treatment on thewafer W, the controller 100 controls the gas box 40 and the gas supplysystem 110 so that the processing gas flowing through each of the supplypaths is supplied to the gas diffusion zones 37 c, 37 e, and 37 v at apredetermined ratio. FIG. 5 shows an example of the ratio of theprocessing gas according to the embodiment. FIG. 5 shows an example of asplit ratio of the processing gas that is supplied through one supplypath to the gas diffusion chambers 37 c, 37 e, and 37 v. The controller100 controls the gas box 40 to supply the processing gas from the gasbox 40 at a predetermined flow rate. Then, in the example of FIG. 5 ,the controller 100 controls the gas supply system 110 to split the flowrate of the processing gas supplied from the gas box 40 such that 5% ofthe processing gas is supplied to the gas diffusion zone 37 c, 80% ofthe processing gas is supplied to the gas diffusion zone 37 e, and 15%of the processing gas is supplied to the gas diffusion zone 37 v. Thisflow split control of the processing gas will now be described.

FIG. 6 shows an example of the flow split control of the processing gasaccording to the embodiment. In the example of FIG. 6 , for the sake ofsimplicity of description, the supply paths for supplying the firstprocessing gas to the gas diffusion zones 37 c and 37 e is illustrated.

When the flow rate control valves 131 c and 131 e are fully opened, thesupply on/off valves 132 c and 132 e are opened, and the exhaust on/offvalves 135 c and 135 e are closed, the first processing gas suppliedfrom the gas box 40 is injected to the processing space S through thegas diffusion zones 37 c and 37 e. When the total flow rate of the firstprocessing gas supplied from the gas box 40 is denoted by Q, the flowrate of the first processing gas supplied to the gas diffusion zone 37 cis denoted by Qc, and the first processing gas supplied to the gasdiffusion zone 37 e is denoted by Qe, the following equation (1) isestablished for the flow rate.

$\begin{matrix}{Q = {{Qc} + {Qe}}} & {{Eq}.\mspace{14mu}(1)}\end{matrix}$

The total flow rate Q can be controlled to a predetermined flow rate bythe flow rate controller of the gas box 40. Thus, in the flow splitcontrol of the present embodiment, the flow rates Qc and Qe arecontrolled by controlling the flow rate ratio instead of controlling thespecifically determined values therefor.

Here, in the gas diffusion zones 37 c, 37 e, and 37 v, there is acorresponding relationship between the pressure of the supplied gas andthe flow rate of the supplied gas. FIG. 7 shows an example of arelationship between a pressure and a flow rate of the gas according tothe embodiment. FIG. 7 shows P-Q characteristics showing therelationship between the pressure (P) and the flow rate (Q) when N₂ gasis supplied. “Center” indicates the P-Q characteristics of the gasdiffusion zone 37 c. “Edge” indicates the P-Q characteristics of the gasdiffusion zone 37 e.

In the plasma processing apparatus 10, a gas is supplied to each of thegas diffusion zones 37 c, 37 e, and 37 v in advance to acquire therelationship between the pressure and the flow rate of the gas. Forexample, in the plasma processing apparatus 10, N₂ gas is supplied fromthe gas box 40 to the gas diffusion zone 37 c at various flow rates, andthen the pressure is measured by the pressure gauge 141 c for each flowrate. Thus, the relationship between the pressure and the flow rate isacquired. In the plasma processing apparatus 10, P-Q characteristic datafor each of the gas diffusion zones 37 c, 37 e, and 37 v is generatedfrom the acquired relationship between the pressure and the flow rate,and the generated P-Q characteristic data is stored in the storage unit103. The P-Q characteristic data may be stored in the storage unit 103from an external source.

Here, in the plasma processing apparatus 10 according to the presentembodiment, the supply on/off valves 132 c, 132 e, 134 c, and 134 e andthe exhaust on/off valves 135 c, 135 e, 136 c, and 136 e are providedwith the orifices 138, respectively. Each orifice 138 is provided toprevent the flow rate controller of the gas box 40 from being affectedby conductance on the upper electrode 30 side. If the diameter of theorifice 138 is excessively reduced, a pressure of the secondary side ofthe flow rate controller of the gas box 40 will increase. Therefore,there is a limit to the amount of diameter reduction. In each of the gasdiffusion zones 37 c, 37 e, and 37 v, when the diameter of the orifice138 is small, a difference in P-Q characteristics may occur due to theinfluence of the pressure of the secondary side. Therefore, it ispreferable to store the P-Q characteristic data of each of the gasdiffusion zones 37 c, 37 e, and 37 v.

The controller 100 controls the gas box 40 and the gas supply system 110so that the processing gas is supplied to the gas diffusion zones 37 c,37 e, and 37 v at a predetermined ratio. For example, the processcontroller 101 controls the gas box 40 to supply one gas or a gasmixture of various gases mixed at respective predetermined flow rates.The process controller 101 obtains the total flow rate of the processinggas. For example, when the gas box 40 supplies the processing gas inwhich the gases A, B, and C are mixed at the following flow rates, thetotal flow rate of the processing gas is as follows:

Gas A: Flow rate 350 sccm

Gas B: Flow rate 150 sccm

Gas C: Flow rate 100 sccm

Total flow rate: 600 sccm.

The process controller 101 obtains the split flow rates of theprocessing gas supplied to the gas diffusion zones 37 c, 37 e, and 37 vwhen the total flow rate of the processing gas, which is supplied to thegas diffusion zones 37 c, 37 e, and 37 v, is divided into apredetermined split ratio. For example, when the processing gas suppliedfrom the gas box 40 is split into the gas diffusion zone 37 c and thegas diffusion zone 37 e at the split ratio of 80:20, the processing gasis supplied to the gas diffusion zone 37 c at 480 sccm, and theprocessing gas is supplied to the gas diffusion zone 37 e at 120 sccm.

The process controller 101 obtains, from the P-Q characteristic datastored in the storage unit 103, the pressure of the processing gas ineach of the gas diffusion zones 37 c, 37 e, and 37 v when supplying theprocessing gas at the determined split flow rates to the gas diffusionzones 37 c, 37 e, and 37 v. Then, the process controller 101 obtains thepressure ratio of the processing gas in the gas diffusion zones 37 c, 37e, and 37 v. For example, in the P-Q characteristic data, the pressureis 40 Torr when the gas is supplied to the gas diffusion zone 37 c at480 sccm, and the pressure is 12 Torr when the gas is supplied to thegas diffusion zone 37 e at 120 sccm. Thus, the pressure ratio of the gasdiffusion zone 37 c to the gas diffusion zone 37 e is 3.33 (=40/12).

The process controller 101 performs pressure ratio control so that theprocessing gas is supplied to the gas diffusion zones 37 c, 37 e, and 37v at the obtained pressure ratio. For example, the process controller101 controls the opening degrees of the flow rate control valves 131 cand 131 e so that the pressure ratio of the gas diffusion zone 37 c tothe gas diffusion zone 37 e measured by the pressure gauges 141 c and141 e becomes 3.33. For example, the process controller 101 controls theopening degrees of the flow rate control valves 131 c and 131 e so thatthe pressure of the gas diffusion zone 37 e becomes 20 Torr when thepressure of the gas diffusion zone 37 c is 66 Torr.

As described above, in the plasma processing apparatus 10, theprocessing gas can be supplied to the gas diffusion zones 37 c, 37 e,and 37 v at a predetermined ratio by performing pressure ratio control.

The controller 100 performs a plasma treatment(s) by switching theprocessing gas(es) while controlling the pressure ratio of theprocessing gas for each supply path. For example, when the atomic layeretching is performed, the process controller 101 controls the gas supplysystem 110 to alternately supply the first processing gas and the secondprocessing gas while performing pressure ratio control such that each ofthe first processing gas and the second processing gas is supplied at apredetermined ratio.

FIGS. 8A and 8B show a switching operation of the gas supply systemaccording to the embodiment. FIGS. 8A and 8B show the configurations ofthe supply paths for supplying the first processing gas and the secondprocessing gas used for atomic layer etching. In the examples of FIGS.8A and 8B, for the sake of simplicity of description, only the supplypaths for supplying the processing gas to the gas diffusion zones 37 cand 37 e are illustrated, and the supply path for supplying theprocessing gas to the gas diffusion zone 37 v is omitted.

FIG. 8A shows a case where the first processing gas is supplied to thegas diffusion zones 37 c and 37 e. FIG. 8B shows a case where the secondprocessing gas is supplied to the gas diffusion zones 37 c and 37 e.When the first processing gas is supplied to the gas diffusion zones 37c and 37 e, the process controller 101 controls the supply on/off valves132 c and 132 e and the exhaust on/off valves 136 c and 136 e to beopened, as shown in FIG. 8A. Further, the process controller 101controls the supply on/off valves 134 c and 134 e and the exhaust on/offvalves 135 c and 135 e to be closed. As a result, the first processinggas is supplied to the gas diffusion zones 37 c and 37 e. Further, thesecond processing gas is exhausted.

The process controller 101 controls the opening degrees of the flow ratecontrol valves 131 c and 131 e through pressure ratio control based onthe pressures of the first processing gas measured by the pressuregauges 141 c and 141 e. Further, the process controller 101 controls theopening degrees of the flow rate control valves 133 c and 133 e throughpressure ratio control based on the pressures of the second processinggas measured by the pressure gauges 142 c and 142 e.

When the gas supplied to the gas diffusion zones 37 c and 37 e isswitched from the first processing gas to the second processing gas, theprocess controller 101 switches the supply on/off valves 132 c and 132 eand the exhaust on/off valves 136 c and 136 e from the open state to theclosed state. Further, the process controller 101 switches the supplyon/off valves 134 c and 134 e and the exhaust on/off valves 135 c and135 e from the closed state to the open state. As a result, as shown inFIG. 8B, the second processing gas is supplied to the gas diffusionzones 37 c and 37 e, and the first processing gas is exhausted.

The process controller 101 controls the opening degrees of the flow ratecontrol valves 133 c and 133 e through pressure ratio control based onthe pressures of the second processing gas measured by the pressuregauges 141 c and 141 e. Further, the process controller 101 controls theopening degrees of the flow rate control valves 131 c and 131 e throughpressure ratio control based on the pressures of the first processinggas measured by the pressure gauges 142 c and 142 e.

The process controller 101 switches the supply on/off valves 134 c and134 e and the exhaust on/off valves 135 c and 135 e from the open stateto the closed state when the gas supplied to the gas diffusion zones 37c and 37 e is switched from the second processing gas to the firstprocessing gas. Further, the process controller 101 switches the supplyon/off valves 132 c and 132 e and the exhaust on/off valves 136 c and136 e from the closed state to the open state. As a result, as shown inFIG. 8A, the first processing gas is supplied to the gas diffusion zones37 c and 37 e, and the second processing gas is exhausted.

Here, in the gas supply system 110 according to the present embodiment,when the ON/OFF switching of the supply on/off valves 132 c and 132 eand the ON/OFF switching of the supply on/off valves 134 c and 134 e areperformed simultaneously, there is a possibility that the supply pathsof the first processing gas and the second processing gas becomeconnected to each other. Therefore, when the ON/OFF switching of thesupply on/off valves 132 c and 132 e and the ON/OFF switching of thesupply on/off valves 134 c and 134 e are performed, it is preferable toinclude a delay time when switching so that there is a period in whichboth of the supply on/off valves 132 c and 132 e and the supply on/offvalves 134 c and 134 e are in the closed state.

When the gas supplied to the gas diffusion zones 37 c and 37 e isswitched from the first processing gas to the second processing gas, theprocess controller 101 provides the period in which both of the supplyon/off valves 132 c and 132 e and the supply on/off valves 134 c and 134e are in the closed state. For example, the process controller 101 firstswitches the supply on/off valves 132 c and 132 e from the open state tothe closed state, and then switches the supply on/off valves 134 c and134 e from the closed state to the open state. Further, the processcontroller 101 also provides the period in which both of the supplyon/off valves 132 c and 132 e and the supply on/off valves 134 c and 134e are in the closed state when switching the gas supplied to the gasdiffusion zones 37 c and 37 e from the second processing gas to thefirst processing gas. For example, the process controller 101 firstswitches the supply on/off valves 134 c and 134 e from the open state tothe closed state, and then switches the supply on/off valves 132 c and132 e from the closed state to the open state.

Meanwhile, in the case of performing the switching between the firstprocessing gas and the second processing gas, a backflow of aswitched-out processing gas (a previously supplied processing gas) mayoccur due to the pressure difference when a pressure of the switched-outprocessing gas that remains on the upper electrode 30 side is higherthan a pressure of a switched-in processing gas (a currently switchedprocessing gas).

FIGS. 9A to 9C are views for explaining the backflow of the processinggas. For example, as shown in FIG. 9A, the first processing gas at apressure of 60 Torr is supplied to the gas diffusion zone 37 c. Pressureratio control is performed for the second processing gas so that thesecond processing gas at a pressure of 20 Torr is to be supplied. At theswitching timing, the supply on/off valve 132 c is switched from theopen state to the closed state and the supply on/off valve 134 c isswitched from the closed state to the open state. In this case, thepressure difference causes the backflow of the first processing gas tothe gas supply line 114 c, as shown in FIG. 9B. The second processinggas allows the first processing gas flowing back to the gas supply line114 c to flow into the gas diffusion zone 37 c, and thereafter thesecond processing gas at a pressure of 20 Torr is supplied into the gasdiffusion zone 37 c, as shown in FIG. 9C. Thus, when the backflow of thefirst processing gas occurs as described above, the pressure ratio ofthe second processing gas changes.

Therefore, when the switching between the first processing gas and thesecond processing gas is performed, the controller 100 controls the gassupply system 110 such that an initial pressure of the switched-inprocessing gas is equal to or higher than a pressure of the switched-outprocessing gas that remains on the upper electrode 30 side.

FIGS. 10A and 10B show an example of a pressure control in the switchingoperation of the gas supply system according to the embodiment. FIGS.10A and 10B show the configuration of the supply paths for supplying thefirst processing gas and the second processing gas used for the atomiclayer etching. In the examples of FIGS. 10A and 10B, for the sake ofsimplicity of description, only the supply paths for supplying theprocessing gas to the gas diffusion zones 37 c and 37 e are illustrated,and the supply path for supplying the processing gas to the gasdiffusion zone 37 v is omitted.

In the example of FIG. 10A, the pressure of the first processing gas iscontrolled through pressure ratio control such that the pressure of thefirst processing gas measured by the pressure gauge 141 c is 60 Torr andthe pressure of the first processing gas measured by the pressure gauge141 e is 80 Torr.

When the gas supplied to the gas diffusion zones 37 c and 37 e isswitched from the first processing gas to the second processing gas, theprocess controller 101 controls the exhaust flow rate control valves 137c and 137 e to have predetermined initial opening degrees, respectively.Each initial opening degree is set to an opening degree at which thesame characteristics as the exhaust characteristics of the upperelectrode 30 are obtained. For example, the initial opening degree ofthe exhaust flow rate control valve 137 c is set such that aconductance, which is substantially the same as a conductance wheninjecting the gas from the gas diffusion zone 37 c, is obtained. Theinitial opening degree of the exhaust flow rate control valve 137 e isset such that a conductance, which is substantially the same as aconductance when injecting the gas from the gas diffusion zone 37 e, isobtained. The initial opening degrees are measured and stored in thestorage unit 103 in advance.

The process controller 101 controls the opening degrees of the flow ratecontrol valves 133 c and 133 e through pressure ratio control based onthe pressures of the second processing gas measured by the pressuregauges 142 c and 142 e. Accordingly, as shown in FIG. 10A, the pressureof the second processing gas measured by the pressure gauge 142 cbecomes 50 Torr, and the pressure of the second processing gas measuredby the pressure gauge 142 e becomes 30 Torr. By performing pressureratio control for the exhaust flow rate control valves 137 c and 137 eto have the initial opening degrees, the opening degrees of the flowrate control valves 133 c and 133 e can be adjusted such that the sameconductance as the conductance when supplying the second processing gasto the gas diffusion zones 37 c and 37 e is obtained. Therefore, evenwhen the gas supplied to the gas diffusion zones 37 c and 37 e isswitched from the first processing gas to the second processing gas, thesecond processing gas can be stably supplied to the gas diffusion zones37 c and 37 e (and 37 v) at a predetermined ratio.

Thereafter, the process controller 101 performs an opening degreeadjustment for closing the exhaust flow rate control valves 137 c and137 e or changing the opening degrees of the exhaust flow rate controlvalves 137 c and 137 e to small degrees. By closing the exhaust side orreducing the opening degree of the exhaust side, the pressures of thesecond processing gas increase at the upstream sides of the exhaust flowrate control valves 137 c and 137 e in the supply paths of the secondprocessing gas. For example, as shown in FIG. 10B, the pressure of thesecond processing gas measured by the pressure gauge 142 c is increasedto 60 Torr and the pressure of the second processing gas measured by thepressure gauge 142 e is increased to 80 Torr. When the pressures of thepressure gauges 142 c and 142 e become equal to or higher than thepressures of the pressure gauges 141 c and 141 e, respectively, theprocess controller 101 switches the supply on/off valves 132 c and 132 efrom the open state to the closed state and switches the supply on/offvalves 134 c and 134 e from the closed state to the open state. Forexample, as shown in FIG. 10B, the process controller 101 performs theswitching control when the pressures of the pressure gauges 142 c and142 e become equal to the pressures of the pressure gauges 141 c and 141e, respectively.

On the other hand, when the gas supplied to the gas diffusion zones 37 cand 37 e is switched from the second processing gas to the firstprocessing gas, the process controller 101 controls the exhaust flowrate control valves 137 c and 137 e to have the initial opening.

The process controller 101 controls the opening degrees of the flow ratecontrol valves 131 c and 131 e through pressure ratio control based onthe pressures of the first processing gas measured by the pressuregauges 142 c and 142 e. Thereafter, the process controller 101 performsan opening degree adjustment for closing the exhaust flow rate controlvalves 137 c and 137 e or changing the opening degrees of the exhaustflow rate control valves 137 c and 137 e to small degrees. By closingthe exhaust side or reducing the opening degree of the exhaust side, thepressures of the first processing gas increase at the upstream sides ofthe exhaust flow rate control valves 137 c and 137 e in the supply pathsof the first processing gas. When the pressures of the pressure gauges142 c and 142 e becomes equal to or higher than the pressures of thepressure gauges 141 c and 141 e, respectively, the process controller101 performs the switching control to switch the supply on/off valves134 c and 134 e from the open state to the closed state and switch thesupply on/off valves 132 c and 132 e from the closed state to the openstate.

Therefore, when the switching between the first processing gas and thesecond processing gas is performed, it is possible to suppress theoccurrence of the backflow of the switched-out processing gas.

The controller 100 may control the gas supply system 110 such that theinitial pressure of the switched-in processing gas is sufficientlyhigher than the pressure of the switched-out processing gas that remainson the upper electrode 30 side.

FIG. 11 shows an example of a pressure control in the switchingoperation of the gas supply system according to the embodiment. FIG. 11shows the configuration of the supply paths for supplying the firstprocessing gas and the second processing gas used for the atomic layeretching. In the example of FIG. 11 , for the sake of simplicity ofdescription, only the supply paths for supplying the processing gas tothe gas diffusion zones 37 c and 37 e are illustrated, and the supplypath for supplying the processing gas to the gas diffusion zone 37 v isomitted.

For example, the process controller 101 controls the opening degrees ofthe flow rate control valves 133 c and 133 e through pressure ratiocontrol based on the pressures of the second processing gas measured bythe pressure gauges 142 c and 142 e. Thereafter, the process controller101 performs an opening degree adjustment for closing the exhaust flowrate control valves 137 c and 137 e or changing the opening degrees ofthe exhaust flow rate control valves 137 c and 137 e to small degrees.By closing the exhaust side or reducing the opening degree of theexhaust side, the pressures of the second processing gas increase at theupstream sides of the exhaust flow rate control valves 137 c and 137 ein the supply paths of the second processing gas. When the pressures ofthe pressure gauges 142 c and 142 e become a predetermined multiple ofthe pressures of the pressure gauges 141 c and 141 e, respectively, theprocess controller 101 performs the switching control. For example, asshown in FIG. 11 , the process controller 101 performs the switchingcontrol at the timing when the pressures P of the pressure gauges 142 cand 142 e respectively become twice the pressure Pc of the pressuregauge 141 c and the pressure Pe of the pressure gauge 141 e.

The relationship between the pressure P and the pressure Pc is definedby the following equation (2):

$\begin{matrix}{{{Pc} \times {Vc}} = {\alpha \times P \times V}} & {{Eq}.\mspace{14mu}(2)}\end{matrix}$

where Vc is the volume of the gas diffusion zone 37 c and V is thevolume of the gas exhaust line.

In the equation (2), α is a parameter of the index of the gas supplyrate and is set to have a value larger than 1, for example.

Therefore, when the switching between the first processing gas and thesecond processing gas is performed, the switched-in processing gas canbe rapidly injected from the upper electrode 30. Further, a periodduring which the switched-out processing gas remains in the upperelectrode 30 can be shortened.

(Control Method of the Gas Supply System)

Next, an example of a control flow of the control method of the gassupply system 110 executed by the plasma processing apparatus 10 will bedescribed. FIGS. 12A to 12G show an example of the control flow of thecontrol method of the gas supply system according to the embodiment. Inthe examples of FIGS. 12A to 12G, for the sake of simplicity ofdescription, only the supply paths for supplying the processing gas tothe gas diffusion zones 37 c and 37 e are illustrated, and the supplypath for supplying the processing gas to the gas diffusion zone 37 v isomitted. FIGS. 12A to 12G show the flow of switching the gas supplied tothe gas diffusion zones 37 c and 37 e from the first processing gas tothe second processing gas.

When the first processing gas is supplied to the gas diffusion zones 37c and 37 e, the process controller 101 controls the valves of the gassupply system 110 as follows (step S1):

Flow rate control valve 131 c: Pressure ratio control

Flow rate control valve 133 c: No control

Flow rate control valve 131 e: Pressure ratio control

Flow rate control valve 133 e: No control

Supply on/off valve 132 c: Open state

Exhaust on/off valve 135 c: Closed state

Supply on/off Valve 132 e: Open state

Exhaust on/off valve 135 e: Closed state

Supply on/off valve 134 c: Closed state

Exhaust on/off valve 136 c: Closed state

Supply on/off valve 134 e: Closed state

Exhaust on/off valve 136 e: Closed state

Exhaust flow rate control valve 137 c: Initial opening degree

Exhaust Flow rate control valve 137 e: initial opening degree.

FIG. 12A shows the states of the valves of the gas supply system 110 instep S1. In step S1, the first processing gas is supplied to the gasdiffusion zones 37 c and 37 e.

When the gas supplied to the gas diffusion zones 37 c and 37 e isswitched from the first processing gas to the second processing gas, theprocess controller 101 controls the valves of the gas supply system 110as follows (step S2):

Flow rate control valve 131 c: Pressure ratio control

Flow rate control valve 133 c: Pressure ratio control

Flow rate control valve 131 e: Pressure ratio control

Flow rate control valve 133 e: Pressure ratio control

Supply on/off valve 132 c: Open state

Exhaust on/off valve 135 c: Closed state

Supply on/off Valve 132 e: Open state

Exhaust on/off valve 135 e: Closed state

Supply on/off valve 134 c: Closed state

Exhaust on/off valve 136 c: Open state

Supply on/off valve 134 e: Closed state

Exhaust on/off valve 136 e: Open state

Exhaust flow rate control valve 137 c: Initial opening degree

Exhaust Flow rate control valve 137 e: initial opening degree.

FIG. 12B shows the states of the valves of the gas supply system 110 instep S2. In step S2, the opening degrees of the flow rate control valves133 c and 133 e are adjusted by pressure ratio control while the secondprocessing gas is exhausted, so that the second processing gas issupplied at a predetermined ratio.

Next, the process controller 101 controls the valves of the gas supplysystem 110 as follows (step S3):

Flow rate control valve 131 c: Pressure ratio control

Flow rate control valve 133 c: Fixing opening degree when pressure ratiocontrol is stable

Flow rate control valve 131 e: Pressure ratio control

Flow rate control valve 133 e: Fixing opening degree when pressure ratiocontrol is stable

Supply on/off valve 132 c: Open state

Exhaust on/off valve 135 c: Closed state

Supply on/off Valve 132 e: Open state

Exhaust on/off valve 135 e: Closed state

Supply on/off valve 134 c: Closed state

Exhaust on/off valve 136 c: Open state

Supply on/off valve 134 e: Closed state

Exhaust on/off valve 136 e: Open state

Exhaust flow rate control valve 137 c: Initial opening degree

Exhaust Flow rate control valve 137 e: initial opening degree.

FIG. 12C shows the states of the valves of the gas supply system 110 instep S3. In step S3, the opening degrees of the flow rate control valves133 c and 133 e are fixed in a state where the second processing gas issupplied at the predetermined ratio.

Next, the process controller 101 controls the valves of the gas supplysystem 110 as follows (step S4):

Flow rate control valve 131 c: Pressure ratio control

Flow rate control valve 133 c: Fixing opening degree

Flow rate control valve 131 e: Pressure ratio control

Flow rate control valve 133 e: Fixing opening degree

Supply on/off valve 132 c: Open state

Exhaust on/off valve 135 c: Closed state

Supply on/off Valve 132 e: Open state

Exhaust on/off valve 135 e: Closed state

Supply on/off valve 134 c: Closed state

Exhaust on/off valve 136 c: Open state

Supply on/off valve 134 e: Closed state

Exhaust on/off valve 136 e: Open state

Exhaust flow rate control valve 137 c: Closed state or changing tosmaller opening degree

Exhaust Flow rate control valve 137 e: Closed state or changing tosmaller opening degree.

FIG. 12D shows the states of the valves of the gas supply system 110 instep S4. In step S4, the pressure of the second processing gas increasesat the upstream side of each of the exhaust flow rate control valves 137c and 137 e in the second processing gas supply paths.

Next, when the pressures of the pressure gauges 142 c and 142 e becomeequal to or higher than the pressures of the pressure gauges 141 c and141 e, respectively, the process controller 101 controls the valves ofthe gas supply system 110 as follows (step S5):

Flow rate control valve 131 c: Pressure ratio control

Flow rate control valve 133 c: Pressure ratio control

Flow rate control valve 131 e: Pressure ratio control

Flow rate control valve 133 e: Pressure ratio control

Supply on/off valve 132 c: Closed state

Exhaust on/off valve 135 c: Open state

Supply on/off Valve 132 e: Closed state

Exhaust on/off valve 135 e: Open state

Supply on/off valve 134 c: Open state

Exhaust on/off valve 136 c: Closed state

Supply on/off valve 134 e: Open state

Exhaust on/off valve 136 e: Closed state

Exhaust flow rate control valve 137 c: Initial opening degree

Exhaust Flow rate control valve 137 e: initial opening degree.

FIG. 12E shows the state of the valves of the gas supply system 110 instep S5. In step S5, the gas supplied to the gas diffusion zones 37 cand 37 e is switched from the first processing gas to the secondprocessing gas. In the gas supply system 110, since pressure ratiocontrol is performed while exhausting the second processing gas beforethe first processing gas is switched to the second processing gas, thesecond processing gas can be rapidly supplied at a predetermined ratio.

Next, when the gas supplied to the gas diffusion zones 37 c and 37 e isswitched from the second processing gas to the first processing gas, theprocess controller 101 controls the valves of the gas supply system 110as follows (Step S6):

Flow rate control valve 131 c: Fixing opening degree when pressure ratiocontrol is stable

Flow rate control valve 133 c: Pressure ratio control

Flow rate control valve 131 e: Fixing opening degree when pressure ratiocontrol is stable

Flow rate control valve 133 e: Pressure ratio control

Supply on/off valve 132 c: Closed state

Exhaust on/off valve 135 c: Open state

Supply on/off Valve 132 e: Closed state

Exhaust on/off valve 135 e: Open state

Supply on/off valve 134 c: Open state

Exhaust on/off valve 136 c: Closed state

Supply on/off valve 134 e: Open state

Exhaust on/off valve 136 e: Closed state

Exhaust flow rate control valve 137 c: Initial opening degree

Exhaust Flow rate control valve 137 e: initial opening degree.

FIG. 12F shows the states of the valves of the gas supply system 110 instep S6. In step S6, the opening degrees of the flow rate control valves133 c and 133 e are fixed while the first process gas is supplied at apredetermined ratio.

Next, the process controller 101 controls the valves of the gas supplysystem 110 as follows (step S7):

Flow rate control valve 131 c: Fixing opening degree

Flow rate control valve 133 c: Pressure ratio control

Flow rate control valve 131 e: Fixing opening degree

Flow rate control valve 133 e: Pressure ratio control

Supply on/off valve 132 c: Closed state

Exhaust on/off valve 135 c: Open state

Supply on/off Valve 132 e: Closed state

Exhaust on/off valve 135 e: Open state

Supply on/off valve 134 c: Open state

Exhaust on/off valve 136 c: Closed state

Supply on/off valve 134 e: Open state

Exhaust on/off valve 136 e: Closed state

Exhaust flow rate control valve 137 c: Closed state or

changing to smaller opening degree

Exhaust Flow rate control valve 137 e: Closed state or changing tosmaller opening degree.

FIG. 12G shows the states of the valves of the gas supply system 110 instep S7. In step S7, the pressure of the first processing gas increasesat the upstream sides of the exhaust flow rate control valves 137 c and137 e in the supply paths of the first processing gas.

When the pressures of the pressure gauges 142 c and 142 e become equalto or higher than the pressures of the pressure gauges 141 c and 141 e,respectively, the process controller 101 returns to step S2 and controlsthe valves of the gas supply system 110 as described in step S2.Accordingly, the gas supplied to the gas diffusion zones 37 c and 37 eis switched from the second processing gas to the first processing gas.In the gas supply system 110 according to the present embodiment, sincepressure ratio control is performed while exhausting the firstprocessing gas before the second processing gas is switched to the firstprocessing gas, the first processing gas can be rapidly supplied at apredetermined ratio.

As described above, the gas supply system 110 according to the presentembodiment includes the upper electrode 30, the gas supply lines 113 cand 113 e, the gas supply lines 114 c and 114 e, the gas exhaust lines116 c and 116 e, and the gas exhaust lines 117 c and 117 e. The gassupply system 110 further includes the supply on/off valves 132 c and132 e, the supply on/off valves 134 c and 134 e, the exhaust on/offvalves 135 c and 135 e, the exhaust on/off valves 136 c and 136 e, andthe controller 100.

The upper electrode 30 is disposed to face the substrate support 16 onwhich the wafer W is to be placed. The upper electrode 30 injects thesupplied gas from a plurality of injection holes formed on the facingsurface facing the substrate support 16. The gas supply lines 113 c and113 e are connected to the upper electrode 30 and supply the firstprocessing gas. The gas supply lines 114 c and 114 e are connected tothe upper electrode 30 and supply the second processing gas. The gasexhaust lines 116 c and 116 e are branched from the gas supply lines 113c and 113 e, respectively, and exhaust the first processing gas flowingthrough the gas supply lines 113 c and 113 e to the gas exhaustmechanism. The gas exhaust lines 117 c and 117 e are branched from thegas supply lines 114 c and 114 e, respectively, and exhaust the secondprocessing gas flowing through the gas supply lines 114 c and 114 e tothe gas exhaust mechanism. The supply on/off valves 132 c and 132 e aredisposed at the downstream sides of the branch points 119 c and 119 ewhere the gas exhaust lines 116 c and 116 e are branched from the gassupply lines 113 c and 113 e, respectively, and each of the supplyon/off valves 132 c and 132 e is configured to switch the ON/OFF statesof the gas supply lines 113 c and 113 e. The supply on/off valves 134 cand 134 e are disposed at the downstream sides of the branch points 120c and 120 e where the gas exhaust lines 117 c and 117 e are branchedfrom the gas supply lines 114 c and 114 e, and each of the supply on/offvalves 134 c and 134 e is configured to switch the ON/OFF states of thegas supply lines 114 c and 114 e. Each of the exhaust on/off valves 135c and 135 e is configured to switch the ON/OFF states of the gas exhaustlines 116 c and 116 e. Each of the exhaust on/off valves 136 c and 136 eis configured to switch the ON/OFF states of the gas exhaust lines 117 cand 117 e.

When the gas supplied to the upper electrode 30 is switched from thefirst processing gas to the second processing gas, the controller 100controls the supply on/off valves 132 c and 132 e and the exhaust on/offvalves 136 c and 136 e to be in the open state, and controls the supplyon/off valves 134 c and 134 e and the exhaust on/off valves 135 c and135 e to be in the closed state. Thereafter, the controller 100 controlsthe supply on/off valves 134 c and 134 e and the exhaust on/off valves135 c and 135 e to be in the open state, and controls the supply on/offvalves 132 c and 132 e and the exhaust on/off valves 136 c and 136 e tobe in the closed state. Further, when the gas supplied to the upperelectrode 30 is switched from the second processing gas to the firstprocessing gas, the control unit 100 controls the supply on/off valves134 c and 134 e and the exhaust on/off valves 135 c and 135 e to be inthe open state, and controls the supply on/off valves 132 c and 132 eand the exhaust on/off valves 136 c and 136 e to be in the closed state.

Thereafter, the controller 100 controls the supply on/off valves 132 cand 132 e and the exhaust on/off valves 136 c and 136 e to be in theopen state, and controls the supply on/off valves 134 c and 134 e andthe exhaust on/off valves 135 c and 135 e to be in the closed state.Accordingly, in the gas supply system 110, the processing gas can bestably and rapidly supplied.

Further, in the gas supply system 110 according to the presentembodiment, when the gas supplied to the upper electrode 30 is switchedfrom the first processing gas to the second processing gas, thecontroller 100 switches the supply on/off valves 134 c and 134 e fromthe closed state to the open state after switching the supply on/offvalves 132 c and 132 e from the open state to the closed state. When thegas supplied to the upper electrode 30 is switched from the secondprocessing gas to the first processing gas, the control unit 100switches the supply on/off valve 132 c and 132 e from the closed stateto the open state after switching the supply on/off valves 134 c and 134e from the open state to the closed state. Accordingly, in the gassupply system 110, it is possible to prevent the supply paths of thefirst processing gas and the supply paths of the second processing gasfrom being connected to each other when the gas supplied to the upperelectrode 30 is switched.

Further, in the gas supply system 110 according to the presentembodiment, the gas supply lines 113 c and 113 e are respectivelyconnected to the upper electrode 30 at the downstream sides of thesupply on/off valves 132 c and 132 e and the gas supply lines 114 c and114 e are respectively connected to the upper electrode 30 at thedownstream sides of the supply on/off valves 134 c and 134 e through thecommon lines 115 c and 115 e respectively having the pressure gauges 141c and 141 e. The gas exhaust lines 116 c and 116 e are respectivelyconnected to the gas exhaust mechanism at the downstream sides of theexhaust on/off valves 135 c and 135 e and the gas supply lines 117 c and117 e are respectively connected to the gas exhaust mechanism at thedownstream sides of the exhaust on/off valves 136 c and 136 e throughthe common lines 118 c and 118 e respectively having the pressure gauges142 c and 142 e. The common lines 118 c and 118 e are respectivelyprovided with the exhaust flow rate control valves 137 c and 137 e,which are configured to adjust the opening degrees thereof, at thedownstream sides of the pressure gauges 142 c and 142 e. The gas supplylines 113 c and 113 e are respectively provided with first supply flowrate control valves, which are configured to adjust the opening degreesthereof, at the upstream sides of the branch points where the gasexhaust lines 116 c and 116 e are branched. The gas supply lines 114 cand 114 e are respectively provided with second supply flow rate controlvalves, which are configured to adjust the opening degrees thereof, atthe upstream sides of the branch points where the gas exhaust lines 117c and 117 e are branched.

When the gas supplied to the upper electrode 30 is switched from thefirst processing gas to the second processing gas, the controller 100controls the opening degrees of the exhaust flow rate control valves 137c and 137 e to correspond to the conductance when the gas is injectedfrom the upper electrode 30. The controller 100 respectively controlsthe opening degrees of the second supply flow rate control valves sothat the pressures of the pressure gauges 142 c and 142 e become thepressures corresponding to the flow rates of the second processing gas.

Thereafter, the controller 100 respectively controls the opening degreesof the exhaust flow rate control valves 137 c and 137 e so that theexhaust flow rate control valves 137 c and 137 e are in the closed stateor the opening degrees thereof is adjusted to small degrees. When thepressures of the pressure gauges 142 c and 142 e become equal to orhigher than the pressures of the pressure gauges 141 c and 141 e,respectively, the controller 100 switches the supply on/off valves 132 cand 132 e from the open state to the closed state and switches thesupply on/off valves 134 c and 134 e from the closed state to the openstate.

In addition, when the gas supplied to the upper electrode 30 is switchedfrom the second processing gas to the first processing gas, thecontroller 100 controls the exhaust flow rate control valves 137 c and137 e to correspond to the conductance when the gas is injected from theupper electrode 30. The controller 100 respectively controls the openingdegrees of the first supply flow rate control valves so that thepressures of the pressure gauges 142 c and 142 e become the pressurescorresponding to the flow rate of the first processing gas.

Thereafter, the controller 100 respectively controls the opening degreesof the exhaust flow rate control valves 137 c and 137 e so that theexhaust flow rate control valves 137 c and 137 e are in the closed orthe opening degrees thereof is adjusted to a small degree. When thepressures of the pressure gauges 142 c and 142 e become equal to orhigher than the pressures of the pressure gauges 141 c and 141 e,respectively, the controller 100 switches the supply on/off valves 134 cand 134 e from the open state to the closed state and switches thesupply on/off valves 132 c and 132 e from the closed state to the openstate. Accordingly, in the gas supply system 110, when the switchingbetween the first processing gas and the second processing gas isperformed, it is possible to suppress the occurrence of the backflow ofthe switched-out processing gas.

Further, in the gas supply system 110 according to the presentembodiment, the inner space of the upper electrode 30 is divided intothe gas diffusion zones 37 c and 37 e, and the gas diffusion zones 37 cand 37 e are connected to the gas injection holes so that the gassupplied to the gas diffusion zones 37 c and 37 e is injected from thegas injection holes connected to the corresponding gas diffusion zones37 c and 37 e. The gas supply system 110 includes, for the gas diffusionzones of the upper electrode 30, the gas supply lines 113 c and 113 e,the gas supply lines 114 c and 114 e, the gas exhaust lines 116 c and116 e, the gas exhaust lines 117 c and 117 e, the supply on/off valves132 c and 132 e, the supply on/off valves 134 c and 134 e, the exhauston/off valves 135 c and 135 e, and the exhaust on/off valves 136 c and136 e, respectively. Accordingly, in the gas supply system 110 accordingto the present embodiment, it is possible to stably and rapidly switchand inject the processing gas from the gas injection holes communicatingwith the gas diffusion zones 37 c and 37 e.

Further, in the gas supply system 110 according to the presentembodiment, the controller 100 obtains the pressures of the processinggas respectively corresponding to the flow rates of the processing gassupplied to the gas diffusion zones 37 c and 37 e of the upper electrode30 based on the characteristic data indicating the relationship betweenthe flow rate and the pressure of the processing gas. The controller 100controls so that the processing gas is split to the gas diffusion zonesof the upper electrode 30 at the obtained pressure ratio of theprocessing gas.

Accordingly, in the gas supply system 110 according to the presentembodiment, it is possible to split the processing gas into the gasdiffusion zones 37 c and 37 at a stable ratio even when the total flowrate of the processing gas changes.

The presently disclosed embodiments are considered in all respects to beillustrative and not restrictive. The above-described embodiments can beembodied in various forms. Further, the above-described embodiments maybe omitted, replaced, or changed in various forms without departing fromthe scope of the appended claims and the gist thereof.

For example, in the above-described embodiments, the case where the gassupply system 110 is used for the atomic layer etching in which thefirst processing gas and the second processing gas are alternatelysupplied has been described as an example. However, the presentdisclosure is not limited thereto. The gas supply system 110 may be usedfor any treatment as long as the treatment is performed by alternatelysupplying the first processing gas and the second processing gas. Forexample, the gas supply system 110 may be used for atomic layerdeposition (ALD) in which a film is formed by alternately supplying thefirst processing gas and the second processing gas.

Further, in the above-described embodiments, the case where the plasmaprocessing apparatus 10 is a plasma etching apparatus has been describedas an example. However, the present disclosure is not limited thereto.The plasma processing apparatus 10 may be a film forming apparatus thatperforms a film formation using plasma or a modification apparatus thatperforms modification of film quality and the like.

Further, in the above-described embodiments, the case where the plasmaetching is performed as the plasma treatment has been described as anexample. However, the present disclosure is not limited thereto. Theplasma treatment may be any treatment using plasma.

Further, in the above-described embodiments, the case where the targetobject is the wafer W has been described as an example. However, thepresent disclosure is not limited thereto. The target object may be anysubstrate such as a glass substrate.

DESCRIPTION OF REFERENCE NUMERALS

-   -   10: plasma processing apparatus    -   16: substrate support    -   30: upper electrode    -   100: controller    -   101: process controller    -   102: user interface    -   103: storage unit    -   110: gas supply system    -   113 c, 113 e: gas supply line    -   114 c, 114 e: gas supply line    -   115 c, 115 e: common line    -   116 c, 116 e: gas exhaust line    -   118 c, 118 e: common line    -   117 c, 117 e: gas exhaust line    -   132 c, 132 e: supply on/off valve    -   134 c, 134 e: supply on/off valve    -   135 c, 135 e: Exhaust on/off valve    -   136 c, 136 e: Exhaust on/off valve    -   137 c, 137 e: Exhaust flow rate control valve    -   141 c, 141 e: pressure gauge    -   142 c, 142 e: pressure gauge    -   W: wafer

The invention claimed is:
 1. A plasma processing apparatus comprising: agas supply system; a chamber having a shower head, at least one gasinjection hole connected to the gas supply system, and at least one gasexhaust port connected to an exhaust mechanism; a substrate supportdisposed in the chamber and configured to support a substrate having anetching target film; a power supply for plasma generation; and acontroller, wherein the gas supply system includes: a first gas supplyline that is connected to the at least one gas injection port and afirst gas source and configured to supply a first processing gas intothe chamber; a second gas supply line that is connected to the at leastone gas injection port and a second gas source and configured to supplya second processing gas into the chamber; a first gas exhaust line thatis branched from the first gas supply line and configured to exhaust thefirst processing gas flowing through the first gas supply line to anoutside of the chamber; a second gas exhaust line that is branched fromthe second gas supply line and configured to exhaust the secondprocessing gas flowing through the second gas supply line to the outsideof the chamber; a first supply on/off valve that is disposed at adownstream side of a branch point of the first gas supply line where thefirst gas exhaust line is branched and configured to switch an ON/OFFstate of the first gas supply line; a second supply on/off valve that isdisposed at a downstream side of a branch point of the second gas supplyline where the second gas exhaust line is branched and configured toswitch an ON/OFF state of the second gas supply line; a first exhauston/off valve configured to switch an ON/OFF state of the first gasexhaust line; and a second exhaust on/off valve configured to switch anON/OFF state of the second gas exhaust line, wherein the controller isconfigured to perform: (a) disposing the substrate on the substratesupport; (b) controlling the first supply on/off valve and the secondexhaust on/off valve to be in an open state and the second supply on/offvalve and the first exhaust on/off valve to be in a closed state andsupplying the first processing gas into the chamber to adsorb anadsorbate generated based on the first processing gas on the substrate;(c) controlling the second supply on/off valve and the first exhauston/off valve to be in the open state and the first supply on/off valveand the second exhaust on/off valve to be in the closed state andsupplying the second processing gas into the chamber to activate theadsorbate; (d) repeating (b) and (c); when switching from (b) to (c),controlling the first supply on/off valve and the second exhaust on/offvalve to be in a closed state and the second supply on/off valve and thefirst exhaust on/off valve to be in an open state; and when switchingfrom (c) to (b), controlling the second supply on/off valve and thefirst exhaust on/off valve to be in the closed state and the firstsupply on/off valve and the second exhaust on/off valve to be in theopen state.
 2. The plasma processing apparatus of claim 1, wherein thecontroller is configured to perform: exhausting the second processinggas to the outside of the chamber during (b); and exhausting the firstprocessing gas to the outside of the chamber during (c).
 3. The plasmaprocessing apparatus of claim 1, wherein, when switching from (b) to(c), the controller controls the second supply on/off valve and thefirst exhaust on/off valve to be in an open state after the first supplyon/off valve and the second exhaust on/off valve to be in a closedstate.
 4. The plasma processing apparatus of claim 1, wherein, whenswitching from (c) to (b), the controller controls the first supplyon/off valve and the second exhaust on/off valve to be in the open stateafter the second supply on/off valve and the first exhaust on/off valveto be in the closed state.
 5. The plasma processing apparatus of claim1, wherein, when switching from (b) to (c) or switching from (c) to (b),the controller controls the gas supply system such that an initialpressure of a switched-in processing gas is equal to or higher than apressure of a switched-out processing gas that remains in the showerhead.
 6. The plasma processing apparatus of claim 1, wherein the firstgas supply line and the second gas supply line are connected to the atleast one gas injection hole through a common line.
 7. The plasmaprocessing apparatus of claim 6, wherein the common line has a pressuregauge for measuring a pressure of a gas supplied to the shower head. 8.The plasma processing apparatus of claim 1, wherein the controller isconfigured to perform etching of the substrate during (c).
 9. The plasmaprocessing apparatus of claim 1, wherein the controller is configured toform a film on the substrate during (c).
 10. The plasma processingapparatus of claim 1, wherein the first gas supply line is connected tothe at least one gas injection hole at a downstream side of the firstsupply on/off valve and the second gas supply line is connected to theat least one gas injection hole at a downstream side of the secondsupply on/off valve through a first common line having a first pressuregauge, the first gas exhaust line is connected to the outside of thechamber at a downstream side of the first exhaust on/off valve and thesecond gas exhaust line is connected to the outside of the chamber at adownstream side of the second exhaust on/off valve through a secondcommon line having a second pressure gauge, the second common line isprovided with an exhaust flow rate control valve, which is configured toadjust an opening degree thereof, at a downstream side of the secondpressure gauge, the first gas supply line is provided with a firstsupply flow rate control valve, which is configured to adjust an openingdegree thereof, at an upstream side of the branch point where the firstgas exhaust line is branched, and the second gas supply line is providedwith a second supply flow rate control valve, which is configured toadjust an opening degree thereof, at an upstream side of the branchpoint where the second gas exhaust line is branched, wherein whenswitching from (b) to (c), the controller controls the opening degree ofthe exhaust flow rate control valve to correspond to a conductance whena gas is injected from the at least one gas injection hole, and theopening degree of the second supply flow rate control valve so that apressure of the second pressure gauge becomes a pressure correspondingto a flow rate of the second processing gas and, thereafter, thecontroller controls the opening degree of the exhaust flow rate controlvalve to close the exhaust flow rate control valve or adjust the openingdegree of the exhaust flow rate control valve to a small degree and,then, when the pressure of the second pressure gauge becomes equal to orhigher than a pressure of the first pressure gauge, the controllerswitches the first supply on/off valve from the open state to the closedstate and switches the second supply on/off valve from the closed stateto the open state, and wherein when switching from (c) to (b), thecontroller controls the opening degree of the exhaust flow rate controlvalve to correspond to a conductance when the gas is injected from theat least one gas injection hole, and the opening degree of the firstsupply flow rate control valve so that a pressure of the second pressuregauge becomes a pressure corresponding to a flow rate of the firstprocessing gas and, thereafter, the controller controls the openingdegree of the exhaust flow rate control valve to close the exhaust flowrate control valve or adjust the opening degree of the exhaust flow ratecontrol valve to a small degree and, then, when the pressure of thesecond pressure gauge becomes equal to or higher than a pressure of thefirst pressure gauge, the controller switches the second supply on/offvalve from the open state to the closed state and switches the firstsupply on/off valve from the closed state to the open state.
 11. Theplasma processing apparatus of claim 1, wherein an inner space of theshower head is divided into a plurality of spaces, the respective spacescommunicate with the at least one gas injection hole so that the gassupplied to each of the spaces is injected from at least one gasinjection hole communicating with the corresponding space, and the firstgas supply line, the second gas supply line, the first gas exhaust line,the second gas exhaust line, the first supply on/off valve, the secondsupply on/off valve, the first exhaust on/off valve, and the secondexhaust on/off valve are provided for each of the spaces of the showerhead.
 12. The plasma processing apparatus of claim 11, wherein thecontroller obtains pressures of the first processing gas or the secondprocessing gas respectively corresponding to flow rates of theprocessing gas supplied to the spaces of the shower head based oncharacteristic data indicating a relationship between the flow rate andthe pressure of the processing gas, and the controller controls so thatthe processing gas is split to the spaces of the shower head at theobtained pressure ratio of the processing gas.
 13. A control method fora plasma processing apparatus, wherein the plasma processing apparatusincludes: a gas supply system; a chamber having a shower head, at leastone gas injection hole connected to the gas supply system, and at leastone gas exhaust port connected to an exhaust mechanism; a substratesupport disposed in the chamber and configured to support a substratehaving an etching target film; a power supply for plasma generation; anda controller, wherein the gas supply system includes: a first gas supplyline that is connected to the at least one gas injection hole and afirst gas source and configured to supply a first processing gas intothe chamber; a second gas supply line that is connected to the at leastone gas injection hole and a second gas source and configured to supplya second processing gas into the chamber; a first gas exhaust line thatis branched from the first gas supply line and configured to exhaust thefirst processing gas flowing through the first gas supply line to anoutside of the chamber; a second gas exhaust line that is branched fromthe second gas supply line and configured to exhaust the secondprocessing gas flowing through the second gas supply line to the outsideof the chamber; a first supply on/off valve that is disposed at adownstream side of a branch point of the first gas supply line where thefirst gas exhaust line is branched and configured to switch an ON/OFFstate of the first gas supply line; a second supply on/off valve that isdisposed at a downstream side of a branch point of the second gas supplyline where the second gas exhaust line is branched and configured toswitch an ON/OFF state of the second gas supply line; a first exhauston/off valve configured to switch an ON/OFF state of the first gasexhaust line; and a second exhaust on/off valve configured to switch anON/OFF state of the second gas exhaust line, the control methodcomprising: (a) disposing the substrate on the substrate support; (b)controlling the first supply on/off valve and the second exhaust on/offvalve to be in an open state and the second supply on/off valve and thefirst exhaust on/off valve to be in a closed state and supplying thefirst processing gas into the chamber to adsorb an adsorbate generatedbased on the first processing gas on the substrate; (c) controlling thesecond supply on/off valve and the first exhaust on/off valve to be inthe open state and the first supply on/off valve and the second exhauston/off valve to be in the closed state and supplying the secondprocessing gas into the chamber to activate the adsorbate; (d) repeating(b) and (c); when switching from (b) to (c), controlling the firstsupply on/off valve and the second exhaust on/off valve to be in aclosed state and the second supply on/off valve and the first exhauston/off valve to be in an open state; and when switching from (c) to (b),controlling the second supply on/off valve and the first exhaust on/offvalve to be in the closed state and the first supply on/off valve andthe second exhaust on/off valve to be in the open state.